COLORADO SPRINGS, Colo. (KKTV) -UPDATE 7/19/18:Nearly three months later, the fire at the Colorado Springs Airport has been ruled accidental.

CSFD firefighters responded to a three-alarm fire at the Colorado Springs Airport overnight. Photo from KKTV.

Investigators say a construction crew working on the roof started it.They were using propane torches to apply tar and the roof caught fire.

With heightened security at airports worldwide, the fire department says this investigation needed the extra time.

"That's why it takes longer than a typical we figure it was a cigarette and it burned up the side of the house. This is something that is on the mind of people in our country and around the world. So it's important and make sure there is no investigation or criminal act,” CSFD Capt. Brian Vaughan said.

Repairs are expected to be finished in time for the busy Thanksgiving travel weekend.

The repairs were expected to cost $5.6 million dollars.

_____________________ORIGINAL STORY 4/25/18:A three-alarm fire at the Colorado Springs Airport grounded all flights and forced the entire building to evacuate on April 16. Fifty-six flights were impacted before the airport reopened about a full day after the blaze was put out.

It took firefighters more than four hours to contain the flames, which broke out on the roof on the west side of the airport. The fire was declared fully contained just after 3 a.m.

Now, the airport can move forward with repairs. Tuesday, roughly a week after the fire, Colorado Springs City Council unanimously approved the spending that will come from airport funds. The estimated cost to fix everything is $5 million after the blaze left heavy smoke damage and water damage from the sprinkler system.

The airport expects all of the damage to eventually be covered by insurance, so taxpayers won't have to cover anything. It also won't impact flight costs.

Since the fire, the airport has already spent about $350,000 in repairs. For flyer safety, they've had fans and continue to monitor the air quality, which has been good since reopening.

"I was just downstairs working at Avis Budget [car rentals]," employee Tony Frost told 11 News following the fire. "All of a sudden, some guy runs downstairs screaming that there's a fire. I thought it was a joke at first."

"There was an announcement that just said, 'Colorado Springs Airport, evacuate the airport now,'" said Dannika Roggie, who was picking someone up.

Frost, Roggie and everyone else in the airport immediately cleared the building, while inbound travelers found themselves suddenly trapped on their planes.

"We ended up sitting on the tarmac for about three hours," passenger Maddison Russell told 11 News.

Lt. Doug Pape with the Colorado Springs Fire Department said firefighters could see flames shooting from the roof before they even got to the airport.

"As we were approaching, we could see the flames from several miles off ... there was quite a bit of smoke production."

More than 60 firefighters battled the blaze. Pape described the firefight:

"We set up our aerial ladder and attacked the fire from the outside. Then we sent crews to the inside to make sure we didn't have any fire to the inside of the building."

He said firefighters were met with several obstacles as they worked to extinguish the fire.

"Challenges was water supply. We had to do relay pumping to aerial operations ... locating the fire, finding the extent and the nature of the fire, and just access was probably the biggest issue. We have water supply, but there wasn't any right in front of us like there would be for a house fire, so we had to have a fairly long lay-in. That delayed a little bit, the operations of getting water on the fire."

Pape said the fire was in the insulation of the roofing material, which can sometimes hide smoldering areas.

"To make sure that we were completely out on such a large structure, we took our time making sure we had no re-ignition," he said of why it took crews so long to get the fire out.

The airport now continues to run without impact to flights.

Investigators are still trying to figure out what started the fire. Firefighters hope to have the cause released by the end of the week.

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